NON-NITRITE AND NON-MOLYBDATE INHIBITORS FOR CLOSED LOOP SYSTEMS

Abstract

Methods and compositions for inhibiting corrosion in closed loop systems in which a heat transfer fluid is recirculated. A combination of a C6-C14 dicarboxylic acid and C6-C14 monocarboxylic acid is added to the recirculating fluid in a weight ratio of from 10:1 to 1:2.

Claims

1. A method of treating a closed loop system in which a fluid is recirculated to inhibit corrosion, the method including: combining with the fluid a C6-C14 dicarboxylic acid and a C6-C14 monocarboxylic acid such that the dicarboxylic acid and monocarboxylic acid are present in the fluid in a weight ratio of from 10:1 to 1:2.

2. The method according to claim 1, wherein the dicarboxylic acid and the monocarboxylic acid are present in the fluid in a weight ratio of from 3:1 to 1:1.

3. The method according to claim 1, wherein the dicarboxylic acid and the monocarboxylic acid are present in the fluid in a weight ratio of from 2.5:1 to 1.5:1.

4. The method according to claim 1, wherein the dicarboxylic acid includes a C8-C12 dicarboxylic acid, and the monocarboxylic acid includes a C8-C12 monocarboxylic acid.

5. The method according to claim 1, wherein at least one of the dicarboxylic acid and monocarboxylic acid includes an aromatic group.

6. The method of claim 4, wherein the dicarboxylic acid includes sebacic acid.

7. The method of claim 4, wherein the dicarboxylic acid includes 2,6-napthalene dicarboxylic acid.

8. The method of claim 4, wherein the monocarboxylic acid includes octanoic acid.

9. The method of claim 4, wherein the monocarboxylic acid includes decanoic acid.

10. The method of claim 1, wherein the dicarboxylic acid is combined with the fluid in an amount that is in a range of from 1 ppm to 5000 ppm.

11. The method of claim 1, wherein the monocarboxylic acid is combined with the fluid in an amount that is in a range of from 10 ppm to 1000 ppm.

12. The method of claim 1, further including combining solvent polymaleic acid (PMA-s) with the fluid.

13. The method of claim 12, wherein the PMA-s and the dicarboxylic acid component are combined with the fluid in a weight ratio of from 1:4 to 1:100.

14. The method of claim 1, further including combining an azole with the fluid.

15. The method of claim 1, further including combining a buffer with the fluid.

16. The method of claim 1, further including combining an inert chemical tracer with the fluid in a known ratio with the dicarboxylic acid and/or monocarboxylic acid.

17. The method of claim 1, wherein the dicarboxylic acid and the monocarboxylic acid form a protective film on a metal surface of the closed loop system that is in contact with the fluid.

18. A corrosion inhibitor composition comprising: (i) water and/or glycol; (ii) a C6-C14 dicarboxylic acid; (iii) a C6-C14 monocarboxylic acid; and (iv) solvent polymaleic acid (PMA-s).

19. The composition of claim 18, wherein the composition further includes an azole.

20. The composition of claim 18, wherein the composition further includes a base and a buffer.

21. The composition of claim 18, wherein the composition includes from 0.5 wt. % to 30 wt. % of the dicarboxylic acid and from 0.25 wt. % to 15 wt. % of the monocarboxylic acid.

22. The composition of claim 18, wherein the composition includes from 0.05 wt. % to 3 wt. % of the PMA-s.

23. The composition of claim 18, wherein the composition comprises less than 0.2 wt. % of nitrites and less than 0.2 wt. % of molybdates.

24. The composition of claim 18, wherein the composition comprises less than 0.1 wt. % of nitrate, less than 0.1 wt. % of silica, and less than 0.1 wt. % of phosphorous.

25. The composition of claim 24, wherein the composition is non-fouling.

26. The composition of claim 18, wherein the composition is effective to from a protective film on metal surface in contact with a fluid independently of an amount of dissolved oxygen in the fluid.

Description

DETAILED DESCRIPTION OF EMBODIMENTS

[0007] The corrosion inhibitor compositions described herein were discovered to be effective in inhibiting corrosion in closed loop systems over a variety of metallurgies. The closed loop systems can include any aqueous- or glycol-based heat transfer fluids including, e.g., boiler water systems, engine coolant systems, air conditioning chilled water systems, etc.

Corrosion Inhibitor Composition

[0008] The novel corrosion inhibitor composition includes a combination of (i) a dicarboxylic acid component that includes at least one dicarboxylic acid, or corresponding salts or anions thereof; and (ii) a monocarboxylic acid component that includes at least one monocarboxylic acid, or corresponding salts or anions thereof. The dicarboxylic acid component can include a C6-C14 dicarboxylic acid, a C8-C12 dicarboxylic acid, or a C10 carboxylic acid. The dicarboxylic acid can include an aliphatic group and/or aromatic group. Suitable dicarboxylic acids include, for example, adipic acid, pimelic acid, suberic acid, sebacic acid, dodecanedioic acid, and 2,6-napthalene dicarboxylic acid. The monocarboxylic acid component can include a C6-C14 monocarboxylic acid, a C8-C12 monocarboxylic acid, or a C8-C10 monocarboxylic acid. The monocarboxylic acid can be provided as a blend of one or more acids having a different carbon number, e.g., such as a blend of C8-C10 acids. The monocarboxylic acid can include an aliphatic group and/or aromatic group. Suitable monocarboxylic acids include hexanoic acid, 2-ethyl hexanoic acid, heptanoic acid, isoheptanoic acid, octanoic acid, nonanoic acid, neodecanoic acid, decanoic acid, and dodecanoic acid.

[0009] The dicarboxylic acid component and monocarboxylic acid component can be present in the composition in a weight ratio of from 10:1 to 1:2, from 3:1 to 1:1, or from 2.5:1 to 1.5:1, for example.

[0010] The dicarboxylic acid component can be present in the corrosion inhibitor composition in amounts of, for example, from 0.5 wt. % to 30 wt. %, from 1 wt. % to 20 wt. %, or from 3 wt. % to 10 wt. %. The monocarboxylic acid component can be present in the corrosion inhibitor composition in amounts of, for example, from 0.25 wt. % to 15 wt. %, from 0.5 wt. % to 10 wt. %, or from 1 wt. % to 5 wt. %.

[0011] These carboxylic acid-based corrosion inhibitors protect against corrosion by forming a protective film on a metal surface that is in contact with the heat transfer fluid in the closed loop system. Advantageously, the carboxylic-acid inhibitors can function independently of an amount of dissolved oxygen in the fluid, unlike molybdate-based corrosion inhibitors since the carboxylic acid inhibitors do not require dissolved oxygen to form the protective film. In contrast, molybdenum-based corrosion inhibitors, such as sodium molybdate, protect metals by forming a protective oxide layer on the metal surface. Dissolved oxygen plays an important role in forming or enhancing these protective films by oxidizing molybdate to higher oxidation states.

[0012] The corrosion inhibitor composition can also optionally include an azole component as an additional corrosion inhibitor. The azole component includes a heterocyclic compound with a five-membered ring of two carbon atoms and three nitrogen atoms. Examples include tolyltriazole (TT), benzotriazole (BZT), chlorinated tolyltriazoles (CI-TT), and brominated tolytriazoles (Br-TT), for example. The azole component can be present in the treatment composition in an amounts of, for example, of less than 5 wt. %, such as from 0.1 wt. % to 3 wt. %, or from 0.2 wt. % to 1 wt. %.

[0013] The components of the corrosion inhibitor composition can be formulated into a stable formulation using water as a primary solvent. Generally, the corrosion inhibitor composition includes at least 30 wt. % water, such as from 50 to 95 wt. % water, or from 70 wt. % to 90 wt. % water.

[0014] The composition can also include a base, such as potassium hydroxide or sodium hydroxide, in amounts of, for example, from 1 wt. % to 15 wt. % or from 2 wt. % to 10 wt., %. The composition can also include a buffer, such as borax or amine-based buffers such as monoethanolamine or triethanolamine or phosphate buffers, in amounts of, for example, from 0.05 wt. % to 5 wt. %, 0.1 wt. % to 3 wt. %, or from 0.2 wt. % to 1 wt. %. The buffer can be selected and added in amounts so that it is effective to stabilize the pH in the closed loop system for extended periods, e.g., perhaps up to 2 years or more.

[0015] The composition can also optionally include a polymeric dispersant. The polymeric dispersant can be a carboxylic acid polymer such as polymaleic acid. In particular, the polymeric dispersant can be solvent PMA (PMA-s). Solvent PMA is formed from polymerization and hydrolysis of maleic anhydride in the solvent phase, and has a different structure and different properties from PMA prepared in water. In particular solvent PMA has a different molecular weight range and distribution than PMA prepared in water. The polymeric dispersant, such as solvent PMA can be present in the composition in amounts of from, for example, 0.05 wt. % to 3 wt. %, from 0.1 wt. % to 1 wt. %, or from 0.5 wt. % to 0.5 wt. %.

[0016] It has been discovered in connection with this disclosure that the use of solvent PMA in the composition further improves corrosion inhibition, and also dramatically improves the dissolution rate of the dicarboxylic acid component into a stable aqueous formulation. This represents a significant improvement since C6-C14 dicarboxylic acids, such as sebacic acid, are very difficult to get into solution and require a very time consuming process to formulate. The solvent PMA and the dicarboxylic acid component can be present in the composition in a mass ratio of from 1:4 to 1:100, from 1:10 to 1:60, or from 1:12 to 1:30, for example.

[0017] The treatment composition can also include one or more antifoam agents, such as a surfactant, that is effective to reduce foaming. The antifoam agent can be present in the treatment composition in an amount of from 0.01 to 1 wt. % or from 0.05 wt. % to 0.5 wt. %, for example.

[0018] The treatment composition can include less than 0.2 wt. % of one or more of the following inorganic components: nitites, molybdates, nitrates, silica, and phosphorous. The treatment composition may also include less than 0.1 wt. % of any of these inorganic components, and may also be free of these inorganic components. In these embodiments, the carboxylic acid corrosion inhibitor is considered to be non-fouling since it is free of inorganic corrosion inhibitors (e.g., phosphate, nitrite, molybdate, and silica) and the risk of fouling caused by inorganic scale deposition or micro biofouling can be substantially minimized.

Treatment Methods

[0019] This disclosure also provides methods of treating closed loop systems by adding a combination of the dicarboxylic acid component and monocarboxylic acid component, as described above, to the fluid in the closed loop system, optionally together with the azole component, solvent PMA, and/or buffer. The closed loop system includes a fluid that is continuously recirculated in the system for extended periods. In this regard, a closed loop system as used herein refers to a system in which a fluid is recirculated in a loop for an extended period of time without adding significant makeup fluid to the loop or removing blowdown of the loop. Closed loop systems can be characterized in that evaporation does not occur in closed loop cooling systems by design, unlike in open cooling systems. The purpose of a closed loop is to transfer heat, from a process or equipment to a second process or equipment. For example, removing heat from a combustion engine and transferring it to an air cooled radiator or transferring heat from an electric boiler to a plastic injected blow mold.

[0020] The treatment methods have been shown to be effective to provide excellent long term corrosion protection in closed loop systems over a wide variety of metallurgies. The metal surfaces in the closed loop system can be made of metals such as, for example, aluminum or its alloys, copper or its alloys such as brass, and iron or its alloys such as steel.

[0021] The fluid can be cooling water or other aqueous fluid that is predominantly water or can be a glycol-based, which is in contact with corrodible metal surfaces in the system that are part of conduits or equipment. In some cases, the fluid may have a pH that is in a range of from 5 to 12, from 7 to 11, or from 8 to 10, for example. The aqueous fluid can have a temperature in the closed loop system that is maintained in a range of from 25 to 100 C. or from 50 C. to 80 C., for example, and up to 350 C. in pressurized loops. Glycol-based fluids in the closed system can have temperatures of from 25 to 200 C., for example. Aqueous fluids can have a Malk (total alkalinity as CaCo3) in a range of from 5 to 10,000 ppm or from 25 to 250 ppm, for example, can have chlorides in an amount of from 1 ppm to 2000 ppm or from 5 ppm to 100 ppm, for example, and can have sulfate in an amount of from 5 ppm to 100 ppm or from 20 ppm to 50 ppm, for example.

[0022] The treatment methods include adding the corrosion inhibitor composition described above to the closed loop system, or alternatively adding two or more of the separate components of the treatment composition to the closed loop system. The treatment method can include adding the components directly to the fluid that recirculates in the closed loop system, including adding the components to the fluid when the system is offline, while the fluid is circulating, and/or by adding the components to the makeup fluid, for example.

[0023] The treatment methods include adding a sufficient amount of the dicarboxylic acid component described above so that it is present in the recirculating fluid in an amount of at least 1 ppm or at least 5 ppm, such as from 1 ppm to 5,000 ppm, 5 ppm to 1,000 ppm, 10 ppm to 300 ppm, from 20 ppm to 200 ppm, or from 30 ppm to 100 ppm, for example. The treatment methods include adding a sufficient amount of the monocarboxylic acid component described above so that it is present in the recirculating fluid in an amount of at least 0.5 ppm or at least 1 ppm, such as from 0.5 ppm to 1000 ppm, 2 ppm to 500 ppm, 5 ppm to 150 ppm, from 10 ppm to 100 ppm, or from 15 ppm to 75 ppm. The dicarboxylic acid component and monocarboxylic component acid can be combined with the recirculating fluid in the closed loop system in a weight ratio of from 10:1 to 1:2, from 3:1 to 1:1, or from 2.5:1 to 1.5:1, for example.

[0024] Another corrosion inhibitor can also be added to the recirculating fluid to further improve corrosion inhibition. For example, an azole compound can be added. If the azole compound is used, it can be combined with the recirculating fluid in the closed loop system in amounts of from 0.5 ppm to 50 ppm, from 2.5 ppm to 30 ppm, or from 5 ppm to 25 ppm, for example.

[0025] If solvent PMA is used in formulating the treatment composition, the solvent PMA can be combined with the recirculating fluid in an amount of from 0.25 ppm to 50 ppm, from 1 ppm to 20 ppm, or from 2.5 ppm to 10 ppm, for example. The solvent PMA and the dicarboxylic acid component can be combined with the recirculating fluid in the closed loop system in a weight ratio of from 1:4 to 1:100, from 1:10 to 1:60, or from 1:12 to 1:30, for example.

[0026] The methods can provide excellent corrosion inhibition over long periods of time in closed loop systems. For example, even with a single dosing of the corrosion inhibitor, the corrosion rate can be maintained to be less than 1 mpy, less than 0.5 mpy, less than 0.15 mpy, or less 0.10 mpy over at least a consecutive eight hour period.

[0027] In embodiments, the recirculated fluid can be treated to inhibit corrosion without the presence of nitrites and molybdates, or with only insignificant amounts of those components such as less than 0.25 ppm of each.

[0028] In some embodiments, one or more chemical tracers can be blended with the carboxylic acid corrosion inhibitor at a specific ratio or added separately to the fluid in a known ratio with the inhibitor to detect and quantify the amount of inhibitor in the fluid. When there is a loss of inhibitor product from the system due to blowdown or other reasons, the loss can be detected and quantified by quantifying the amount of chemical tracer lost, and a dosing pump can replenish the inhibitor to the desired set point or concentration. The tracer can be an inert chemical tracer that does not react or interact with the chemistries used in the fluid and the treatment composition. PTSA is a suitable fluorescent agent that can be used with the carboxylic acid corrosion inhibitor and can be detected and quantified by a fluorimeter.

EXAMPLES

Corrosion Inhibition Experiment on Mild Steel

[0029] The corrosion inhibition characteristic of two example formulations having the compositions described below are compared with a formulation of a nitrite corrosion inhibitor (40 wt. % sodium nitrite) and a commercially available organic acid product.

Example Composition 1

TABLE-US-00001 C8/C10 Monocarboxylic Acid 6.00 wt. % C10 dicarboxylic acid 14.00 wt. % Azole compound 2.00 wt. % Buffer 4.00 wt. % KOH (50%) 26.40 wt. % PMA-s 0.50 wt. % Antifoam agent 0.10 wt. % RO water Balance

Example Composition 2

TABLE-US-00002 C8/C10 Monocarboxylic Acid 3.00 wt. % C12 dicarboxylic acid 7.00 wt. % Azole compound 1.00 wt. % Buffer 2.00 wt. % KOH (50%) 13.20 wt. % PMA-s 0.25 wt. % Antifoam agent 0.05 wt. % RO water Balance

[0030] To perform the corrosion test, the example corrosion inhibitors, nitrite corrosion inhibitor, and commercially available organic acid corrosion inhibitor are mixed with test water in the amounts shown below. The test water included 35 ppm sulfate, 15 ppm chloride, 50 ppm Malk as CaCO3, and the pH was adjusted to 9.7 with sulfuric acid. Mild steel coupons (C1010 MS) having an exposed surface area of 4.5 cm.sup.2 were submerged in the test water, and subjected to the test parameters shown below, where rotational rate refers to the stir bar speed to simulate a 3 ft/s flow across the metal coupons. A control sample was also tested that included no corrosion inhibitors.

Test Parameters

TABLE-US-00003 Temperature ( C.) 70 Rotational Rate (rpm) 350 Ba (mV/dec) 120 Bc (mV/dec) 120

[0031] The corrosion rate (mpy) is measured hourly over 18 hours, and the average corrosion rate over hours 10-18 is determined. The results are shown below.

TABLE-US-00004 Organic Nitrite Acid Time Ex. 1 Product Product Ex. 1 Ex. 2 (hrs) Control (1250 ppm) (1500 ppm) (3000 ppm) (750 ppm) (1500 ppm) 0 16.77 0.41 0.26 4.08 0.06 0.03 1 13.53 0.35 0.11 3.99 0.19 0.05 2 13.55 0.26 0.08 4.45 0.20 0.08 3 13.08 0.23 0.07 4.15 0.22 0.06 4 12.45 0.19 0.08 3.71 0.16 0.06 5 12.20 0.16 0.05 3.66 0.14 0.07 6 11.53 0.14 0.07 3.60 0.15 0.04 7 10.95 0.15 0.04 3.84 0.14 0.05 8 10.43 0.16 0.07 3.34 0.14 0.09 9 9.99 0.14 0.12 3.25 0.15 0.08 10 9.74 0.15 0.08 3.40 0.15 0.08 11 9.37 0.15 0.14 2.93 0.15 0.09 12 8.77 0.11 0.12 2.74 0.15 0.07 13 8.42 0.09 0.13 2.58 0.08 0.08 14 8.41 0.11 0.12 2.94 0.12 0.09 15 8.12 0.13 0.12 2.77 0.08 0.08 16 7.77 0.12 0.13 2.69 0.08 0.10 17 7.46 0.09 0.08 2.72 0.08 0.07 18 7.44 0.08 0.14 2.41 0.07 0.08 10-18 hr 8.39 0.11 0.12 2.80 0.11 0.08 avg.

[0032] As can be seen, the example corrosion inhibitors exhibit comparable or better corrosion inhibition performance over long durations than conventional corrosion inhibitors. Also, even when used in significantly lower doses (e.g., Ex. 1 at 750 ppm), the corrosion inhibitors exhibit excellent performance.

Corrosion Inhibition Experiment on Several Metallurgies

[0033] The corrosion inhibition characteristics of a third example composition, having the formulation shown below, were measured for a variety of metallurgies.

Example Composition 3

TABLE-US-00005 C8/C10 Monocarboxylic Acid 2.10 wt. % C10 dicarboxylic acid 4.90 wt. % Azole component 0.66 wt. % Buffer 0.66 wt. % KOH (50%) 7.87 wt. % PMA-s 0.33 wt. % Antifoam agent 0.05 wt. % RO water Balance

[0034] In this experiment, the Example 3 composition was dosed at 10 wt. % in water and the corrosion loss (mg) was determined according to the test parameters outlined in ASTM D1384 (2019). A control sample without any corrosion inhibitors was also evaluated. The results are shown below.

TABLE-US-00006 Metal Solder Cast Copper Brass Cast Iron Steel Aluminum Description Loss (mg) Loss (mg) Loss (mg) Loss (mg) Loss (mg) Loss (mg) ASTM D3306 30 max 30 max 10 max 10 max 10 max 10 max Requirement Control 102 13.2 22.2 136.7 276.7 305.5 Ex. 3 7.6 3.2 1.2 0.4 0.8 2.7

[0035] It can be seen from the above results that the compositions and treatments described herein are effective to inhibit corrosion in a wide variety of metallurgies, and showed substantial improvement as compared to the Control sample.

[0036] It will be apparent to those skilled in the art that variations of the methods and compositions described herein are possible and are intended to be encompassed within the scope of the present invention.